Combustion controlled nox reduction method and device

ABSTRACT

In this invention, there is provided a method for reducing NOx emission from an internal combustion engine designed to produce a given amount of power and a method for improving fuel efficiency by providing an intake stream of oxygen-enriched air and keeping the amount of power output the same so that the combustion temperature in the engine is lower.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a Continuation of application Ser. No. 11/600,458filed on Nov. 16, 2006.

BACKGROUND OF INVENTION

1. Field of the Invention

This invention relates generally to methods for reducing NOx emissionfrom a combustion engine and apparatuses thereof.

2. Background Art

NO_(x) (also commonly written as NOx or NOX) is the generic name for agroup of highly reactive gases that contain varying amounts of nitrogenoxides including, but not limited to, NO, NO₂, NO₃, N₂O, N₂O₃, N₂O₄,N₃O₄, and mixtures thereof. They are typically colorless and odorlessbut react readily with ammonia, moisture and other compounds to formnitric acid and related particles. NO_(x) and their related chemicalproducts have been identified as major air pollutants and are the causesfor serious health and environmental concerns in the U.S. and otherindustrialized nations around the world. Some of the heath andenvironmental problems related to NO_(x) include ground level ozone(smog) formed when NO_(x) and volatile organic compounds (VOC) react inheat and sunlight, acid rains formed when NO_(x) and sulfur oxide reactwith other substances in the air to form acids, and deep-penetratingparticles that can exacerbate human respiratory diseases such asemphysema and bronchitis. According to some estimates common sources ofNO_(x) are motor vehicle (49%), electric utilities (27%), and otherindustrial, commercial and residential sources (19%) that burnhydrocarbon fuels.

Among the common sources of NO_(x), motor vehicle has perhaps receivedthe most attention. Since 1970, the U.S. Environmental Protection Agency(EPA) has required motor vehicle manufactures to reduce NO_(x)emissions. Although significant reductions have been achieved throughauto emissions controls, increasing public awareness of environmentalissues has led to ever more stringent regulatory requirements. On Dec.21, 2000, the EPA signed emission standards for model year 2007 andlater heavy-duty highway engines to limit the emission level to about0.20 g/bhp-hr, a ten-fold reduction from the 2004 level. In light of thegreat public interest in reducing NO_(x) emissions, there is an urgentneed for improved means to reduce NO_(x) emissions. Therefore, there isa need for a device, system or method for reducing NO_(x) emissions incombustion engines and for reducing NO_(x) emissions form other NO_(x)producing devices as well.

To address the problem of NO_(x) emissions, an understanding of how NOxis formed may be helpful. During combustion of fossil fuels (mainlyhydrocarbons) NOx is formed via several mechanisms: thermal NO_(x), fuelNO_(x), and prompt NO_(x). Thermal NO_(x) results from the reactionbetween nitrogen in the air and excess oxygen at elevated temperatures.Fuel NO_(x) results when nitrogen is oxidized by combustion air. PromptNO_(x) is caused by the intermediate formation of hydrogen cyanide (HCN)followed by the oxidation of HCN to nitric oxide (NO).

Fuel NO_(x) and prompt NO_(x) are typically not of major concern. FuelNO_(x) are not produced in significant amount from burning ofhydrocarbon fuels, which have little or no chemically bound nitrogen.Moreover, the nitrogen content of fuels can be reduced during theproduction of the fuel using known techniques. Prompt NO_(x) is onlysignificant in very fuel-rich flames and is produced by high-speedreactions in the flame front. Fuel rich flames are not prevalent ininternal combustion engines. These two types of NO_(x) will herein becollectively referred to as chemical NO_(x).

The formation of thermal NO_(x) from a typical combustion reactionconverting fossil fuel into energy is a complex chemical phenomenoninvolving about 1000 chemical reactions with about 100 distinct chemicalspecies. Understanding this complex network of interacting reactions canbe a daunting task and detailed theoretical modeling and prediction ofcombustion remain difficult (for an overview, see Chemical Kinetics andCombustion Modeling. J A Miller, R J Kee, C K Westbrook Annual Review ofPhysical Chemistry, October 1990, Vol. 41, Pages 345-387). However, someof the essential mechanisms of thermal NO_(x) formation (this issometimes referred to as the Zel'dovich mechanism) may be generallyunderstood. A generalized description of the process is set forth below.

At high temperatures, both nitrogen (N₂) and oxygen (O₂) are dissociatedinto atoms that react by the Zel'dovich mechanism:

N₂+O

NO+N

N+O₂

NO+O

N+OH

NO+H

In this process, NO is the principal reaction product. Once nitrogen andoxygen molecules are dissociated into atoms, the indicated threereactions form a chain reaction process that can self-propagate for manycycles, each adding to the amount of NO produced. The major factors thataffect thermal NO_(x) production are combustion temperature, residencetime at temperature, the degree of fuel/air mixing, and theconcentrations of oxygen and nitrogen in that is burned. Highertemperature, longer residence time, enhanced mixing, and higher oxygenconcentration all favor NO_(x) formation.

As mentioned earlier, in addition to transportation related pollution itis known that, industrial, commercial, and residential burners such asused in electric utilities, in commercial factories, and in residentialhome heaters can all so contribute to the increasing globalconcentration of NO_(x). For purposes of this discussion, we will limitour focus primarily to NO_(x) emissions resulting from transportationindustries and particularly motor vehicle combustion engines includingbut not limited to gasoline and diesel engines.

In FIG. 1, a schematic diagram of a typical combustion engine 10 isshown. The engine 10 receives oxidant 12 for the combustion reaction(usually atmospheric air) and fuel 14 through the reactant intake 16.The fuel and oxidant may be fed individually for mixing in the cylinderor may mix in the reactant intake 16. Once the reactants are inside thecombustion chamber 18 of the engine 10, the reactants (air-fuel mixture20) are ignited, as for example with a spark plug 22, during thecompression stroke of the engine 10. The combustion results in therelease of heat energy and expansion of gases that increases thepressure inside the combustion chamber 18. After the combustionreaction, the products of the reaction 24 are released from the chamber18 through engine exhaust passage 26, typically into the atmosphere 30.The reaction products 24, sometimes referred to as exhaust gases, maycontain unburned or partially burned hydrocarbons and also NO_(x) bothof which contribute to pollution when they are exhausted into theatmosphere 30. In some cases the exhaust passage 26 may comprise one ormore devices to reduce the NO_(x) that is discharged into theatmosphere. For example, there may be a scrubber 32 and/or a catalyticconverter 34 included along or at the outlet of the exhaust passage 18.Devices such as scrubber 32 and catalytic converter 34 are designed toextract NO_(x) from the exhaust gas stream 20 after the NO_(x) hasalready been formed. Such devices can be complicated, difficult toinstall on internal combustion engines, and are often expensive.Typically such devices are only partially effective to extract theNO_(x). Unburned hydrocarbon may also be found in the exhaust stream anddifferent means are required for removing hydrocarbon compared to themeans required for removing NO_(x).

Prior to the present invention, much of the research on reduction ofemissions from combustion engines has been primarily focused on eithercompleting combustion of all components of the fuel sources or onimplementing post-combustion clean-up technologies. Complete combustiontypically focuses on burning the fuel at high temperatures and burningthe fuel with high oxidant content so that all the components of thehydrocarbon fuels are fully oxidized. The use of excess oxidant to insure complete combustion is sometimes referred to as lean fuel/air ratioburning (less fuel than stoichiometricly balanced fuel combustion wouldrequire for the available oxygen in the air.) The same situation issometimes referred to as rich air/fuel combustion (more air than isrequired to combine completely with the available fuel). Bothexpressions represent the same situation where the amount of oxidantrequired for complete combustion is greater that the amount of fuelpresent. This is sometimes expressed with an inequality expression as“oxidant>fuel”. Some combustion modification technologies have beenaimed at modifying the complex combustion chemistry such as by injectingadditives into the fuel-mix to lower the production of NO_(x) whilemaintaining complete combustion. One approach to reducing pollution hasbeen to provide an enriched oxygen air stream into an internalcombustion engine to accomplish complete combustion. While increasedoxygen content in the air fuel mixture can decrease the unburnedhydrocarbon pollution in the exhaust, it has been found that theincreased oxidant often also increases the production of NO_(x).

It has also been common to consider post-combustion clean-uptechnologies that are aimed at extracting NO_(x) from the engine exhaustusing devices such as scrubbers and catalytic converters. Maintainingboth complete combustion of the fuel and reduced NO_(x) are oftencompeting goals. In prior devices complete hydrocarbon combustion andengine efficiency often meant that the NO_(x) formation was increasedand scrubbers and/or catalytic converters were relied upon to reduceNO_(x) emissions. Moreover, when using scrubbers and catalyticconverters it has often been necessary to periodically replacing theexpensive scrubbers and converters to ensure NO_(x) extractionefficiency and to provide different, sizes, numbers or types ofscrubbers or converters to upgrade the system to keep up with the latestemission requirements.

SUMMARY OF INVENTION

According to one embodiment of the invention, the inventors havediscovered a novel approach to reducing NO_(x) emission by preciselycontrolling the ratio of N₂ to O₂ in the intake air of an internalcombustion engine to maintain existing engine efficiency and to achievea level of NO_(x) reduction as might be mandated by governmentalagencies, such as the EPA, without requiring expensive upgrades toexisting scrubbers and converters.

According to one embodiment of the present invention, there is provideda method for reducing NO_(x) emission from a combustion engine byfeeding an oxygen-enriched air stream comprising a desired proportion ofoxygen and nitrogen into the intake of an existing internal combustionengine to maintain conversion of fuel to energy that is equivalent tothe designed fuel to energy conversion of the engine while operating ata lowered combustion temperature and reducing the level of NO_(x)formation due to the lowered combustion temperature.

According to one embodiment of the present invention, there is alsoprovided a combustion engine comprising an apparatus capable ofproviding an intake air stream having a desired oxygen/nitrogen ratiofor an internal combustion engine. One skilled in the art will recognizeworkable embodiments of the apparatus to include but not limited to acompressor for providing compressed oxygen to enhance the oxygenconcentration of the intake air, a molecular membrane for separating O₂and N₂ in the air stream so that an enhanced O₂ stream is provided tothe engine intake, a gas separation membrane, a molecular sieve, afilter capable of filtering out oxygen or nitrogen, a gas absorptionseparator, a pressure swing separator and multiples of the forgoingdevices for in creasing the concentration of oxygen and any combinationthereof.

Other aspects and advantages of the invention will be apparent from thefollowing description and the appended claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic representation of a typical combustion engine

FIG. 2 is a graphical representation of a generalized relationshipshowing the percentage of total theoretically possible NO_(x) formationrate as a function of combustion temperature.

FIG. 3 is a graphical representation of a generalized relationshipshowing the percentage of total theoretically possible NO_(x) formationrate as a function of available oxidant (oxygen, O₂).

FIG. 4 is a schematic representation of a combustion engine with aplurality of alternative oxygen enhancers for feeding the fuel and airto the engine for combustion.

FIG. 5 is a graph representing a theoretical relationship betweentemperatures (° K) at which burning takes place by plotting the percentof carbon fuel remaining to be reacted, namely the concentration of thereactants (Ca), versus the time of the reaction at four differentconstant temperatures as indicated in the legend.

FIG. 6 is a graph representing a theoretical relationship betweentemperature (° K) at which burning takes place versus concentration ofoxygen in the reacting gas (X_(B)) that will maintain a constant timeand constant rate of conversion. The starting concentration of O₂ for aconstant time and conversion (completion of the reaction of all thefuel) is indicated, ranging from 1.0 or a standard amount of O₂ in airto 2.0 indicating double the amount of O₂ in air. This indicates thathigher temperatures are required to complete the conversion when thereis a smaller percentage of O₂ an lower temperature can obtain completecombustion

FIG. 7 is a graph representing a theoretical relationship betweentemperature (° K) and time for reacting 20% of the fuel (i.e., the timeand temperature for a combustion reaction to take place and to reach 0.8concentration of carbon (Ca) plotted for each of 5 concentrations ofoxygen in air (X_(B)) ranging from 90% (18% O₂ and 82% N₂), normalconcentration or 100% (21% O₂ and 79% N₂), 120% (25% O₂ and 75% N₂),160% (33% O₂ and 67% N₂), and 200% (42% O₂ and 58% N₂) as indicated inthe legend.

FIG. 8 is a graph of a modeled representing a reaction at a constanttemperature of 980° K and showing the time for reacting all thereactants of the fuel in terms of concentration Ca of a reacting gas.The modeled results are plotted for each of five different startingconcentrations (X_(B)) of O₂ in air. The time to react to an indicatedpercent of remaining reactant concentration (Ca) is plotted for fiveconcentrations (X_(B)) of oxygen in air, as indicated in the legendwhere the smallest concentration X_(B) is 90% of normal concentrationand the largest concentration X_(B) is 200% of normal concentration asfollows for each of the five cases modeled: 90% (O₂=18% and N₂=82%),100% (O₂=21% and N₂=79% N2), 120% (O₂=25% and N₂=75%), 160% (O₂=33% andN₂=67% N2), and 200% (O₂=42% and N₂=58%) as indicated in the legend.

FIG. 9 is a graph of a modeled representing a reaction at a constanttemperature of 990° K and showing the time for reacting all thereactants of the fuel in terms of concentration Ca of a reacting gas.The modeled results are plotted for each of five different startingconcentrations (X_(B)) of O₂ in air. The time to react to an indicatedpercent of remaining reactant concentration (Ca) is plotted for fiveconcentrations (X_(B)) of oxygen in air, as indicated in the legendwhere the smallest concentration X_(B) is 90% of normal concentrationand the largest concentration X_(B) is 200% of normal concentration asfollows for each of the five cases modeled: 90% (O₂=18% and N₂=82%),100% (O₂=21% and N₂=79% N2), 120% (O₂=25% and N₂=75%), 160% (O₂=33% andN₂=67% N2), and 200% (O₂=42% and N₂=58%) as indicated in the legend.

FIG. 10 is a graph of a modeled representing a reaction at a constanttemperature of 1000° K and showing the time for reacting all thereactants of the fuel in terms of concentration Ca of a reacting gas.The modeled results are plotted for each of five different startingconcentrations (X_(B)) of O₂ in air. The time to react to an indicatedpercent of remaining reactant concentration (Ca) is plotted for fiveconcentrations (X_(B)) of oxygen in air, as indicated in the legendwhere the smallest concentration X_(B) is 90% of normal concentrationand the largest concentration X_(B) is 200% of normal concentration asfollows for each of the five cases modeled: 90% (O₂=18% and N₂=82%),100% (O₂=21% and N₂=79% N2), 120% (O₂=25% and N₂=75%), 160% (O₂=33% andN₂=67% N2), and 200% (O₂=42% and N₂=58%) as indicated in the legend.

FIG. 11 is a graph of a modeled representing a reaction at a constanttemperature of 1010° K and showing the time for reacting all thereactants of the fuel in terms of concentration Ca of a reacting gas.The modeled results are plotted for each of five different startingconcentrations (X_(B)) of O₂ in air. The time to react to an indicatedpercent of remaining reactant concentration (Ca) is plotted for fiveconcentrations (X_(B)) of oxygen in air, as indicated in the legendwhere the smallest concentration X_(B) is 90% of normal concentrationand the largest concentration X_(B) is 200% of normal concentration asfollows for each of the five cases modeled: 90% (O₂=18% and N₂=82%),100% (O₂=21% and N₂=79% N2), 120% (O₂=25% and N₂=75%), 160% (O₂=33% andN₂=67% N2), and 200% (O₂=42% and N₂=58%) as indicated in the legend.

FIG. 12 is a graph of a modeled representing a reaction at a constanttemperature of 1020° K and showing the time for reacting all thereactants of the fuel in terms of concentration Ca of a reacting gas.The modeled results are plotted for each of five different startingconcentrations (X_(B)) of O₂ in air. The time to react to an indicatedpercent of remaining reactant concentration (Ca) is plotted for fiveconcentrations (X_(B)) of oxygen in air, as indicated in the legendwhere the smallest concentration X_(B) is 90% of normal concentrationand the largest concentration X_(B) is 200% of normal concentration asfollows for each of the five cases modeled: 90% (O₂=18% and N₂=82%),100% (O₂=21% and N₂=79% N₂), 120% (O₂=25% and N₂=75%), 160% (O₂=33% andN₂=67% N2), and 200% (O₂=42% and N₂=58%) as indicated in the legend.

DETAILED DESCRIPTION

The present invention is primarily concerned with the reduction ofthermal NO_(x) in combustion engines. As such, the following discussionwill be focused on preventing or reducing thermal NO_(x) formation in atypical combustion reaction used to power combustion engines. Althoughother undesirable pollutants such as sulfur oxides (SO_(x)) may also beproduced in a given internal combustion engine, such other pollutantsare not the focus of the useful method and device disclosed and will notbe included in this discussion.

In a combustion reaction of hydrocarbon fossil fuels, all chemical bondsin the hydrocarbon (C_(x)H_(y)) are broken, oxidized, and recombined ata sufficiently high temperature within a reasonably short time period.For some commercially available fuels, temperature above about 900° C.may be sufficient and for almost any commercially available hydrocarbonfuels temperature above 950° C. will be sufficient to break all chemicalbonds to permit oxidation of the hydrocarbon. However, given themultitude of chemical reaction pathways available, a range of reactionproducts are usually produced. To approach theoretical combustion orstoichiometric combustion (the ideal combustion process in which all thecarbon (C) is oxidized to CO₂, all the hydrogen (H) to H₂O, and all thesulfur (S) to SO₂ one may provide O₂ in excess of the stoichiometricallybalanced amount.

A typical generalized chemical equation representing the burning offossil fuels is as shown below in equation (i):

C_(x)H_(y)N_(z1)O_(z2)S_(z3)+ER_(HT)(O₂N₂)→a(CO₂)+b(H₂O)+c(C_(v)H_(w))+[d(SO_(x2))+e(NO_(x))+f(O₂)+g(N₂)]  (i)

-   -   where,

ER _(HT)>1.0  (ii)

-   -   (ER_(HT) is the equivalent ratio of oxidant:fuel for the high        temperature burning);    -   where,

v,w,z1,z2,z3<<x,y;  (iii)

-   -   where, a, b, c, d, e, f, and g are coefficients determined by        the values of v, w, x, y, and z such that the chemical equation        is balanced; and where,

NO_(x) =e(fuel NO_(x))+e2(thermal NO_(x))  (iv)

It will be recognized that CO₂, H₂O, O₂ and N₂ are all “good”environmentally safe resultant components that may be exhausted into theatmosphere generally without being deemed to be harmful to theecological environment. Any amount of remaining hydrocarbon C_(v)H_(w)that is exhausted as emissions is deemed undesirable or “bad”. However,in a typical oxygen rich and fuel lean burning environment whereER_(TH)>1.0 and where the combustion temperature is sufficiently high,it is expected that there will be little if any unburned hydrocarbon andthus the coefficient “e” in equation (iv) will be considered to be equalto 0, or at most will be very small. The SO_(X) and NO_(x) (regardlessof whether it is fuel SO_(X) and/or NO_(x) or thermal SO_(X) and/orNO_(x)) are all potentially “bad” components deemed to be harmful to theecological environment.

Those skilled in the art will recognize from this disclosure that ingeneral, the amount of time required for complete combustion is inreverse proportion to combustion temperature and amounts of oxidant,i.e. the higher the combustion temperature, the shorter the completecombustion time, and, likewise, the higher the amount of availableoxidant, the shorter the complete combustion time.

The rate of combustion might be generally represented as the change infuel concentration during burning as follows:

ΔC _(A) /Δt=KX _(A) X _(B)  (v)

Where ΔC_(A) is the change in fuel concentration,

X_(A) is the concentration of the fuel for the reaction,

X_(B) is the concentration of the oxidant for the reaction, and

K is the conversion rate given by the equation:

K=Ae ^(−E/RT)  (vi)

Where A is a constant known as the frequency factor,

E is a constant known as the activation energy,

R is the gas constant, and T is the temperature of the reaction.

Thus it can be considered that the rate of converting fuel to energy maybe predicted by the equation:

ΔC _(A) /Δt=Δe ^(−E/RT) X _(A) X _(B)  (vii)

It is considered that the power (P) of an engine having a given designis proportional to the rate of conversion of fuel, namely P isproportional to ΔC_(A)/Δt. In the equation for the rate of fuelconversion it is also considered that as RT becomes larger, theexpression—E/RT becomes a smaller negative number and the expressionAe^(−E/RT) becomes larger. Also it will be seen that a largerconcentration of oxidant X_(B) also correlates to a larger value of theexpression Ae^(−E/RT) X_(A) X_(B). Hence, an increase in the rate ofconversion of fuel correlates to either an increase in the temperatureor an increase in the concentration of oxidant. It is noted that theeffect of temperature on the rate of conversion is an exponentialrelationship such that the conversion to NOx increases exponentiallyrelative to increases in the temperature. The effect of oxidantconcentration on the rate of conversion is generally a linearrelationship. The equation bears out common experience that when otherfactors are the same, a higher temperature T will correlate to a fasterthe rate of fuel conversion and greater power. Consider for example, thefollowing common observations to facilitate understanding of theprincipals and effects calculable by equation (vii) as explained above.Thus for example at one high temperature condition, a sufficiently hightemperatures can result in almost instant conversion of fuel as in aflash over or an explosion. In another example at a low condition, asufficiently low temperature (within the range of combustiontemperatures for a fuel/air mixture) will require a long time to burnthe fuel. Also when other factors are the same, higher concentration ofoxidant will allow a faster rate of conversion, such as for example aburning reaction in pure oxygen is observed to be very rapid. Theseexamples are given for understanding of some basic principals and arenot intended to be quantitative for purposes of the disclosure.

Based upon this understanding, it can also be understood that for thesame power output, an increase in the concentration of the oxidant X_(B)can be offset by an appropriate decrease in the temperature T. Thedecrease in temperature T decreases RT and therefore increases theabsolute value of the expression E/RT. In the equation (vii) thisresults in a larger negative value for the exponent, −E/RT. And a largernegative value as an exponent decreases the value of the expressionAe^(−E/RT). Thus, if the concentration of the oxidant, X_(B), isincreased, the same rate of fuel conversion ΔCA/Δt is maintained at alower temperature, T. The power output of an engine is determined by therate at which the engine converts the chemical energy of the fuel tomechanical energy. Thus, it has been found by the inventors that byincreasing the oxidant concentration, X_(B), the same power output(proportional to the fuel conversion rate, ΔCA/Δt), can be maintainedfrom a given engine at a lower reaction temperature, T. This assumesthat the same mechanical efficiencies of the engine are obtained atlower operating temperatures, and this is considered to be a goodassumption for most engines as it is for most mechanical devices.

As the inventors have pointed out above, a reduction in the combustiontemperature, T, also causes a reduction in NO_(X) formation. The sameamount of fuel is converted to exhaust products in the same amount oftime so that a slower rate of NO_(X) formation also means that the totalNO_(X) formation will be reduced over time. Also, because the rate ofNO_(X) formation is exponentially related to the combustion temperature,T, at the higher combustion temperature ranges small reductions intemperature represent large reductions in NO_(X) formation. The presentinvention recognizes that this relationship can be used to a significantadvantage for the reduction of NO_(X) produced by substantially anygiven engine design. According to a useful embodiment of the invention,an engine designed to burn fuel in air and to operate at a particulartemperature to produce a particular output power can be modified tooperate at the same power output and at a lower temperature byincreasing the proportion of oxygen present in the air.

In a typical air aspirated hydrocarbon fuel burning engine, such as agasoline fuel burning internal combustion engine, a diesel fuel internalcombustion engine, or a natural gas internal combustion engine, thecombustion temperature is around 1000° C.-1100° C. This temperature isgenerally considered to be sufficient to break the chemical bonds ofnitrogen and oxygen and to initiate the Zel'dovich mechanism ofcombustion.

FIG. 2 shows a representative graph for a hydrocarbon fuel combusted inair of the percentage of NO_(x) formation relative to the total possibleNO_(x) formation that would be possible based upon the available O₂ as afunction of combustion temperature. This is analogous to the rate offormation as a function of combustion temperature. When the combustiontemperature is below about 700° C., the formation rate of NO_(x) is at aminimum. Once the combustion temperature rises above the threshold ofNO_(x) formation temperature at about 700° C. for this fuel, theformation rate of NO_(x) begins to increase rapidly. In this examplerepresentation of a hydrocarbon fuel, such as natural gas, gasoline, ordiesel fuel, at temperatures between about 1000° C.-1100° C., theformation of NO_(x) hits a steep portion of an exponentially increasingcurve. At combustion temperatures close to 1100° C., nearly 100% of thepossible NO_(x) formation is considered as being achieve, and attemperatures at or above about 1100° C., 100% of the possible NO_(x) isdeemed to be achieved.

FIG. 3 shows a generalized graph of NO_(x) formation rate as a functionof available oxidant (in this example the oxidant availability is interms of concentration of oxygen or O₂ in air). It can be seen that atboth low oxygen availability and high oxygen availability (indicatingthat there would be a depletion of N₂); formation of NO_(x) is less thanits maximum potential. However, it can also be seen that there is anintermediate range of available oxygen for which NO_(x) formation is ata maximum. Thus, solely for the purpose of reducing NO_(x), it isdesirable to keep combustion temperature below 1000° C., preferablybelow 700° C. and to keep oxygen supply either at a high availabilitylevel or at a low availability level.

Understandably, the primary purpose of an internal combustion engine isnot to reduce NO_(x) formation; rather it is to convert chemical energyinto mechanical energy by completely burning the fuel in the air. Otherconsiderations are also taken into account, such as the considerationthat burning hydrocarbon fuels generally requires operating temperaturesabove about 900° C. for efficient burning. Likewise, keeping theavailable oxygen too low can result in starving the combustion reactionof required oxidant, and keeping oxygen availability in high excess isoften not practical when operating an engine. Particularly, internalcombustion engines that are designed for operation on Earth benefit fromusing the currently abundant air supply. Since naturally occurring airon Earth is composed of about 79% nitrogen and only about 21% oxygen,using air as the supply of oxidant for a combustion engine normallyestablishes the concentration of oxidant. Supplying a steady stream ofoxygen in great excess of stoichiometric proportion is thereforegenerally expensive or generally requires a significant amount of energyinput to produce a very high concentration of oxygen. It was previouslynot generally believed to be practical or possible to reduce NO_(x)formation in a combustion engine by way of enriching oxygen in theintake air. It was commonly believed that oxygen in great excess ofstoichiometric amounts was required in order to achieve significantreduction.

Referring to FIG. 4 it will be understood that when a fuel is burnedinside the combustion chamber of an engine 20, it is converted into hightemperature product gases. The volume occupied by the gases increasesand/or the pressure inside the engine combustion chamber increases.Generally, it will be understood by those skilled in the art that themechanism for converting the chemical energy to mechanical energy is byusing the increase in combustion chamber 21 pressure applied within thecylinder 22 and between the closed cylinder head 23 and the movablepiston 24. The increased volume and pressure of the burning gases pushesthe piston 24 and this allows the engine to capture the chemical energyin the form of piston movement to accommodate the increased pressure andvolume of the gasses translated through a connecting rod 25 to rotarymotion 26 at power output crank shaft (not shown). The time period overwhich the burning occurs to cause the piston to move down one strokelength S of the cylinder determines the conversion rate of the fuel. Thetime period is determined by the rotation speed of the engine or therevolutions per minute (RPM) at which the engine operates. Whendesigning an engine, the designer or engineers use the displacementvolume of the piston moving in the cylinder, as determined by the borediameter B and the stroke length S, and the time for burning, asdetermined by the operating RPM, to provide a desired or acceptableoperating temperature. To maximize the power for a given size engine,the combustion temperature is generally desired to be as high aspossible within acceptable ranges of the materials and coolingcapability of the cylinder and piston. If an engine is designed towithstand a higher temperature and to rotate at a higher speed it willgenerally produce more power. In the past much effort was directed toincreasing the rate of combustion in order to increase the power. Thishas generally resulted in higher operating temperatures and thetemperatures may be higher and higher as the materials and coolingsystem capabilities are improved.

A factor that must also be considered is the efficiency of the engine.FIG. 5 shows a graph of fuel conversion rate Ca as a function of timeunder constant temperature conditions. Each of the curves represent theconversion rate of fuel using atmospheric air as the source of oxidantand at the constant temperatures of 995° K, 1000° K, 1005° K, and 1010°K for each line as indicated in the legend. The power of the engine isclosely related to the rate of fuel conversion.

It will be understood that the faster the combusting gases expand(namely the faster the fuel conversion occurs), the greater the rate ofincrease in pressure with in the cylinder between the combustion chamberand the piston. Increased pressure results in faster the piston movementand greater power output from the engine. On the other hand, the sameengine operating at a slower fuel conversion rate would ordinarilyresult in producing less power from that same engine. It has beendiscovered by the inventors that generally internal combustion enginesare designed to produce a particular output power and the designedoutput power is related to and basically establishes the combustiontemperature for any given engine design. The inventors have found thatthe operating temperature has a significant effect on the NO_(x)formation. However, to run an engine at a lower temperature than thedesigned combustion temperature would result in inefficient fuel energyconversion and less than the designed output power. This analysisassumes that in either instance of high or low temperature engineoperation the amount of fuel to be burned has within it the samechemical energy and a stoichiometric amount of air is supplied to theengine for complete combustion (or for the same degree of completenessof combustion).

One way to operate an engine at a slower fuel conversion rate is toprovide less fuel to be converted during a specified period of time.However, that would result in less available chemical energy. Anotherway to provide a slower conversion rate is to operate at a lowertemperature. This aspect of engine operation is further illustrated inFIG. 5 where theoretical fuel conversion percentage Ca is plotted as afunction of time for different constant temperature conditions, asindicated by the legend.

It has been found by the inventors that a lower temperature of areaction may also be obtained by increasing the concentration of oxidantin the air without increasing the power output. This might bedemonstrated in FIG. 6, plotting the effect of increasing theconcentration of oxygen in air from the normal 21% O₂, at X_(B), =1 upto 42% O₂, at X_(B)=2. The reaction temperatures in this theoreticalexample decreases from 1010° K down to 990° K to obtain the samecompletion of a reaction within a same time. From this figure, it can beunderstood that an engine operating under lower than normal oxygenintake conditions would require a higher temperature to reach 100% fuelconversion, whereas the same engine operating under an enriched oxygenintake condition would require a lower temperature to achieve 100% fuelconversion in the same amount of time.

According to one embodiment of the present invention, there is provideda method for reducing NO_(x) emission from a combustion engine byfeeding an oxygen-enriched air stream into the intake of an existinginternal combustion engine, wherein the enriched air stream comprises adesired proportion of oxygen and nitrogen such that the oxygenconcentration is at a higher than the normal concentration for which theengine was designed. For a given engine design output power thecombustion temperature is lowered from the designed operatingtemperature and the same output power is produced because the fuelconversion rate is maintained by correspondingly increasing theconcentration of oxygen. A lower temperature results due to theincreased rate of fuel conversion provided by the increased availabilityof oxidant. Thus, because the combustion temperature is lower than thedesigned combustion temperature for the designed output power, the levelof NO_(x) formation is also reduced. It will be noted that this iscontrary to the results of others where it was determined that theNO_(x) formation was increased by the increased oxidant concentration toincrease the power.

In one embodiment the desired proportion of oxygen/nitrogen depends onthe type of fuel, the reduced amount of NO_(x) desired, and the relativecosts associated with increasing the oxidant concentration above thatnormally found in atmospheric air. One example of a useful ratio ofoxygen/nitrogen is about 5% enrichment of oxygen content, or modifiedintake air comprising about 25% oxygen and 75% nitrogen. According toone aspect of the invention it has been found by the inventors thatenrichment of oxidant in the intake air stream has a greater effect onNO_(x) reducing the amount of NO_(x) formation than would be expectedbased only upon the reduction of the amount of nitrogen. It might havebeen considered impractical to supply a stream of oxygen in sufficientexcess of the stoichiometric amount to enjoy the beneficial NO_(x) ratereduction effect as shown in FIG. 3 due only to the effect of lessnitrogen available for forming NO_(x). There would need to be almostcomplete elimination of N₂ from the intake stream (i.e., nearly pureoxygen) in order to observe a significant reduction of thermal NOx.However, the inventors have discovered that it is not necessary tosupply oxygen in great excess of stoichiometric amount. In this presentinvention, the inventors have found that the combined effect of lowertemperature and higher oxygen content can yield a significant reductionin NO_(x) emission. For example, using the diagram of FIG. 2, it mightbe understood that by employing 5% oxygen-enriched air, the combustionreaction is shifted to require a lower combustion temperature to achievethe same fuel conversion rate. It is noted that the fuel conversion rateis responsible for the power output. Thus, by maintaining the same poweroutput while increasing the oxidant concentration, the temperature ofcombustion should be reduced. Pointing to FIG. 2, one can see that forhydrocarbon fuel combustion a normal engine design operating temperaturein a range of 1000° C.-1100° C. brackets a steep region of the NO_(x)formation curve. For some examples, lowering the operating temperaturefrom 1100° C. to 1000° C. might correspond to reducing the rate ofNO_(x) formation by as much as about 70%, lowering the operatingtemperature from 1100° C. to 1090° C. might correspond to reducing therate of NO_(x) formation by as much as about 30%, lowering the operatingtemperature from 1100° C. to 1095° C. might correspond to reducing therate of NO_(x) formation by as much about 20%. Simply put, thisindicates that for an existing engine design, a slight change incombustion temperature to a lower operating temperature can result in asignificant reduction in the indicated NO_(x) formation rate. This ispotentially significant where governmental mandated reductions of NO_(x)in emissions by only 5% have in the past been difficult to achieve.

The following Table A shows relative amounts of NO_(x) formation from amodeled combustion process showing burning natural gas at four differentfuel/oxygen concentration levels and at three different temperatures froeach different concentration. The amount of NO_(x) is indicated asapproximately the amount of NO formed because for the process modeled,the quantity of NO formed was two orders of magnitude larger than thenext largest quantity of NO_(x) formed or at least about 100 times asmuch as quantity of the next largest type of NO_(x) (among the commontypes of NO, NO₂, and N₂O) formed in the modeled process.

TABLE A Theoretically Modeled Representation of NO_(x) FormationEstimated NO_(x) formation NO_(x) Formation measured in lb/Hr-lb of fuellbs/hour for Burning (in terms of NO each ton of fuel C_(A) N2/O₂Temperature ° C. formation only) processed C_(A) = 1.0 (approx. N₂ =16/O₂ = 4 1064 °C. 5.35 × 10⁻⁴  1.07 lbs/hr 79% N₂/21% O₂ standard air)C_(A) = 1.0 N₂ = 16/O₂ = 4  850 °C. 1.15 × 10⁻⁴  0.23 lbs/hr C_(A) = 1.0N₂ = 16/O₂ = 4  650 °C. 1.46 × 10⁻⁵ 0.029 lbs/hr C_(A) = 1.2 (approx. N₂= 12/O2 = 4 1064 °C. 4.63 × 10⁻⁴  0.93 lbs/hr 75% N₂/25% O2 standardair) C_(A) = 1.2 N₂ = 12/O2 = 4  850 °C. 1.00 × 10⁻⁴  0.20 lbs/hr C_(A)= 1.2 N₂ = 12/O2 = 4  650 °C. 1.27 × 10⁻⁵ 0.025 lbs/hr C_(A) = 1.5 N₂ =9.33/O2 = 4 1064 °C. 3.90 × 10⁻⁴  0.78 lbs/hr (approx. 70% N2/30% O2standard air) C_(A) = 1.5 N₂ = 9.33/O2 = 4  850 °C. 8.78 × 10⁻⁵  0.18lbs/hr C_(A) = 1.5 N₂ = 9.33/O2 = 4  650 °C. 1.06 × 10⁻⁵ 0.021 lbs/hrC_(A) = 2.5 (approx. N₂ = 4/O2 = 4 1064 °C. 2.69 × 10⁻⁴  0.54 lbs/hr 50%N2/50% O2 standard air) C_(A) = 2.5 N₂ = 4/O2 = 4  850 °C. 8.78 × 10⁻⁵ 0.12 lbs/hr C_(A) = 2.5 N₂ = 4/O2 = 4  650 °C. 5.78 × 10⁻⁵ 0.015 lbs/hr

In certain prior internal combustion engines attempts to obtain greateroutput power or greater efficiency by increasing the concentration ofinput oxygen had the effect of increasing the NO_(x) formation.Applicants have discovered that by attempting to obtain greater outputpower that is greater than the designed output power (i.e. by increasingthe rate of fuel conversion rather than keeping that rate the same)combustion temperature was also increased. As a result the NO_(x)formation rate increased as well. Thus, by maintaining the output powerto be the same while increasing the oxidant concentration thetemperature must be reduced and the NO_(x) formation will becorrespondingly reduced as indicated by the graph of FIG. 2.

According to one embodiment of the present invention, there is alsoprovided a method for improving fuel efficiency of a combustion engine.In a typical combustion engine, most of the energy released from burningthe fuel is dissipated as heat. By using 5% enriched oxygen andoperating the engine at a lower combustion temperature, not only is therate of NO_(x) formation reduced, the rate of energy wasted due to hightemperature heat losses should also be reduced. Thus, less fuel will berequired to obtain the same useful power output generated by burning thefuel at a lower temperature. The amount of fuel burned can therefore bereduced without while maintaining the same useful power output of theengine.

According to one embodiment of the present invention, an oxygenenhancement apparatus provides a stream of oxygen-enriched air to acombustion engine. A schematic of such an oxygen enhancement apparatus30 is shown in FIG. 4. The apparatus comprises a first end 32, a secondend 34 and a middle portion 36. The first end is capable of beingadapted to connect to the intake of a combustion engine 20. The secondend comprised of an interface 38 exposed to an air source. The middleportion is adapted to form a passage 36 connecting the first 32 and thesecond 34 ends. The apparatus typically operates by drawing air from thesecond end 34, passing the air through the middle portion 36, and thenfeeding the air to a combustion engine 20 via the first end 32. In asituation where the air source comprises compressed air, the middleportion 36 may simply serve as a regulating element, controlling theamount of air flow. In a situation where the air source comprisesatmospheric air, the middle portion may further comprise one or moreoxygen-enriching elements that might be generally referred to as an O₂enhancer 40 a. In one embodiment an oxygen enriching element mightinclude an O₂ adder, such as a compressed O₂ source. In otherembodiments the oxygen enhancers may be selected from a group includingbut not limited to a molecular membrane 40 c or gas separation membrane40 c, a molecular sieve 40 d, a filter system 40 e capable of filteringout oxygen or nitrogen out of the air, adsorption materials oradsorption devices 40 f, a pressure swing separator 40 g, and anycombination of one or more of these or other devices for enhancingoxygen content or concentration in air.

According to one embodiment of the present invention, a combustionengine 20 may comprise an in-place enriched air stream apparatus 30capable of providing, an air stream having a desired oxygen/nitrogenratio to an intake 22 of a combustion engine 20. One skilled in the art,based upon the disclosure herein will recognize the usefulness ofadapting an apparatus 30 capable of enriching oxygen content in air tofit onto and interfaces with a combustion engine 20 to provide,oxygen-enriched air 40 for combustion with the fuel 50 for which theengine 20 is designed. Usefully, the in-place enriched air streamapparatus 30 comprises an apparatus that is efficient at enriching orotherwise enhancing the oxygen content of the air 40 by about 1% to 20%over the ambient air 42. Examples of such an apparatus may include butare not limited to one or more apparatuses selected from a group of acompressed O₂ carrier 40 b, a molecular membrane 40 c, a gas separationmembrane 40 c, a molecular sieve 40 d, a system of one or more filters40 e capable of filtering out oxygen or nitrogen, adsorption materials40 f or devices 40 f, pressure swing devices 40 g, other O₂ enhancers 40a and any combinations thereof.

EXAMPLES

The following are graphical representations, similar to the tabularrepresentation in Table A above, showing computer modeled examplecalculations based upon specified input of a hydrocarbon fuel. (Forpurposes of the model natural gas was used as the fuel although it willbe understood that similar representations and relationships may beshown for other hydrocarbon fuels such as diesel and gasoline fuels.)

Specifically, FIG. 5 is a graph representing a theoretical relationshipbetween time of reaction versus concentration of oxygen in the reactinggas (X_(B)) for four different reaction temperatures at which burningtakes place, including 995° K, 1000° K, 1005° K, and 1010° K. Again itwill be observed that the modeled time for reaction is decreased atevery concentration of O₂ by increasing the temperature of the reaction.This relationship is maintained for the entire range of conversionpercentages (note that 0.1 corresponds to 90% completion of fuelconversion Ca.

FIG. 6 is a graph representing a theoretical relationship betweentemperatures (° K) at which burning takes place versus concentration ofoxygen X_(B) in the reacting gas that will maintain a constant time andconstant rate of conversion.

FIG. 7 is a graph representing a theoretical relationship betweentemperature (° K) and time for reacting 20% of the fuel (i.e., the timeand temperature for a combustion reaction to reach 0.8 concentration ofcarbon at each of 5 concentrations of oxygen takes place versusconcentration (X_(B)) of oxygen in air. The modeled results are plottedfor each of five different starting concentrations (X_(B)) of O₂ in air,namely starting concentration (X_(B)) of oxygen in air where thesmallest concentration X_(B) is 90% of normal concentration and thelargest concentration Ca is 200% of normal concentration as follows foreach of the five cases modeled: 90% (O₂=18% and N₂=82%), 100% (O₂=21%and N₂=79%), 120% (O₂=25% and N₂=75%), 160% (O₂=33% and N₂=67%), and200% (O₂=42% and N₂=58%) as indicated in the legend. It will be observedthat over the range of temperatures modeled, the time of reactiondecreased with increased reaction temperature. Also, the time was higherfor lower concentrations of O₂ at every temperature. In only oneinstance, at about 1020° K the time for converting using 0.9concentration of O₂ approached the same time for converting using 1.0concentration of O₂. Never-the-less, the relationship, for allconcentrations greater than standard air, clearly demonstrated that thetime for completing combustion to a desired degree, is shorter forhigher concentration O₂ is shorter

Basically the same relationship of shorter time of conversion as aresult of higher concentration of O2 is demonstrated by all of theGraphs in FIGS. 8-12. These graphical representations show reactions atfive different constant temperatures (one temperature indicated for eachgraph) of FIG. 8 shows a constant 980° K, FIG. 9 shows a constant 990°K, FIG. 10 shows a constant 1000° K, FIG. 11 shows a constant 1010° K,and FIG. 12 shows a constant 1020° K. For each temperature of reactionthe time for reacting is plotted versus the percentage of completion ofthe fuel conversion Ca. At time=0, the level of completion is 0 as theamount of Ca remaining is 1.0. The modeled results are plotted for eachof five different starting concentrations (X_(B)) of O₂ in air, namelystarting concentration (X_(B)) of oxygen in air where the smallestconcentration X_(B) is 90% of normal concentration and the largestconcentration X_(B) is 200% of normal concentration as follows for eachof the five cases modeled: X_(B)=90% (O₂=18% and N₂=82%), X_(B)=100%(O₂=21% and N₂=79%), X_(B)=120% (O₂=25% and N₂=75%), X_(B)=160% (O₂=33%and N₂=67%), and X_(B)=200% (O₂=42% and N₂=58%) as indicated in thelegend. This shows the theoretical effect of the increases in theconcentration of oxygen in the intake air for a given engine and isprovided here for illustrative purposes only and should not be construedas limiting the invention to any one of the representative examples.

FIG. 8 is a graph of a modeled representing a reaction at a constanttemperature of 980° K and showing the time for reacting all of the O₂from the starting concentration indicated as 1.0 to complete combustionindicated as 0 remaining O₂. The modeled results are plotted for each offive different starting concentrations (X_(B)) of O₂ in air, namelystarting concentration (X_(B)) of oxygen in air where the smallestconcentration Ca is 90% of normal concentration and the largestconcentration X_(B) is 200% of normal concentration as follows for eachof the five cases modeled: 90% (O₂=18% and N₂=82%), 100% (O₂=21% andN₂=79%), 120% (O₂=25% and N₂=75%), 160% (O₂=33% and N₂=67%), and 200%(O₂=42% and N₂=58%) as indicated in the legend.

FIG. 9 is a graph of a modeled representing a reaction at a constanttemperature of 990° K and showing the time for reacting all of the O₂from the starting concentration indicated as 1.0 to complete combustionindicated as 0 remaining O₂. The modeled results are plotted for each offive different starting concentrations (X_(B)) of O₂ in air, namelystarting concentration (X_(B)) of oxygen in air where the smallestconcentration Ca is 90% of normal concentration and the largestconcentration X_(B) is 200% of normal concentration as follows for eachof the five cases modeled: 90% (O₂=18% and N₂=82%), 100% (O₂=21% andN₂=79%), 120% (O₂=25% and N₂=75%), 160% (O₂=33% and N₂=67%), and 200%(O₂=42% and N₂=58%) as indicated in the legend.

FIG. 10 is a graph of a modeled representing a reaction at a constanttemperature of 1000° K and showing the time for reacting all of the O₂from the starting concentration indicated as 1.0 to complete combustionindicated as 0 remaining O₂. The modeled results are plotted for each offive different starting concentrations (X_(B)) of O₂ in air, namelystarting concentration (X_(B)) of oxygen in air where the smallestconcentration X_(B) is 90% of normal concentration and the largestconcentration X_(B) is 200% of normal concentration as follows for eachof the five cases modeled: 90% (O₂=18% and N₂=82%), 100% (O₂=21% andN₂=79%), 120% (O₂=25% and N₂=75%), 160% (O₂=33% and N₂=67%), and 200%(O₂=42% and N₂=58%) as indicated in the legend.

FIG. 11 is a graph of a modeled representing a reaction at a constanttemperature of 1010° K and showing the time for reacting all of the O₂from the starting concentration indicated as 1.0 to complete combustionindicated as 0 remaining O₂. The modeled results are plotted for each offive different starting concentrations (X_(B)) of O₂ in air, namelystarting concentration (X_(B)) of oxygen in air where the smallestconcentration X_(B) is 90% of normal concentration and the largestconcentration X_(B) is 200% of normal concentration as follows for eachof the five cases modeled: 90% (O₂=18% and N₂=82%), 100% (O₂=21% andN₂=79%), 120% (O₂=25% and N₂=75%), 160% (O₂=33% and N₂=67%), and 200%(O₂=42% and N₂=58%) as indicated in the legend.

FIG. 12 is a graph of a modeled representing a reaction at a constanttemperature of 1020° K and showing the time for reacting all of the O₂from the starting concentration indicated as 1.0 to complete combustionindicated as 0 remaining O₂. The modeled results are plotted for each offive different starting concentrations (X_(B)) of O₂ in air, namelystarting concentration (X_(B)) of oxygen in air where the smallestconcentration X_(B) is 90% of normal concentration and the largestconcentration X_(B) is 200% of normal concentration as follows for eachof the five cases modeled: 90% (O₂=18% and N₂=82%), 100% (O₂=21% andN₂=79%), 120% (O₂=25% and N₂=75%), 160% (O₂=33% and N₂=67%), and 200%(O₂=42% and N₂=58%) as indicated in the legend.

Thus, there has been disclosed a method and a device for reducing airpollutants from an internal combustion engine of the type designed forproviding a given power output based upon the combustion of hydrocarbonfuel in air. The method includes providing an oxygen-enriched intake airstream to an internal combustion engine, maintaining the output power atthe given power output according to the design of the engine, andcombusting the oxygen enriched air with fuel in the engine at atemperature lower than the normal combustion temperature for the enginewhen burning air having ambient oxygen content so that a rate of fuelenergy conversion results due to the oxygen enriched air at the lowertemperature that is essentially the same rate of fuel energy conversionas would normally result from combusting the fuel with air havingambient oxygen content. By this method the amount of thermal NO_(x)produced in exhaust gas from the engine is reduced due to the lowercombustion temperature, relative to the engine operating at a highertemperature without enhanced oxygen content air the.

In one embodiment of a NOx reduction method and device theoxygen-enriched intake air comprises a mixture of nitrogen and oxygenand the oxygen concentration in the intake air is increased to about 25%oxygen.

In one or more other embodiments of a method or a device for reducingNOx in an internal combustion engine, the oxygen-enriched air stream isprovided by one or more methods or devices of oxygen-air streamenrichment selected from the group of oxygen enrichment methods anddevices including supplying compressed oxygen into the engine air intakeas by a compressed oxygen tank, separating oxygen from the air using amolecular membrane and supplying enriched oxygen intake air into theengine, as by molecular membrane separation of enriched oxygen air fromenriched nitrogen air, supplying enriched oxygen intake air into theengine by separating oxygen and nitrogen gases using a gas separationmembrane, supplying enriched oxygen intake air into the engine byseparating oxygen and nitrogen gases using a molecular sieve, supplyingenriched oxygen intake air into the engine by separating oxygen andnitrogen by using a filter, supplying enriched oxygen intake air intothe engine by separating oxygen and nitrogen by using a gas absorptionseparator, supplying enriched oxygen intake air into the engine byseparating oxygen and nitrogen by using a pressure swing separator, andsupplying enriched oxygen intake air into the engine by separatingoxygen and nitrogen by gases using any combinations the variouslydescribed methods and devices.

In one embodiment a method of improving fuel efficiency in a combustionengine is disclosed including adapting an oxygen-enriching apparatus toa combustion engine, providing an air stream from the oxygen-enrichingapparatus to the combustion engine intake, and combusting fuel with theoxygen-enriched air.

In one embodiment an apparatus for reducing air pollutants fromcombustion engines includes a first end, a second end, and a middleportion, wherein the first end includes a connector capable of beingadapted to the intake of a combustion engine, the second end includes aninterface exposed to an air source; and the middle portion communicatesair from the second end to the first end and includes an oxygenenhancer, such that the air communicated from the air source to theengine has an enhanced oxygen content so that the operating temperaturefor obtaining a given power output is lower than the operatingtemperature without an enhanced oxygen content of the intake air.

In one or more embodiments of an apparatus for reducing air pollutantsfrom combustion engines includes a first end, a second end, and a middleportion, wherein the first end includes a connector capable of beingadapted to the intake of a combustion engine, the second end includes aninterface exposed to an air source; and the middle portion communicatesair from the second end to the first end and includes an oxygenenhancer, wherein the oxygen enhancer of the middle portion furtherincludes one or more oxygen enhancement mechanisms selected from amolecular membrane, a gas separation membrane, a molecular sieve, afilter, a gas absorption separator, a pressure swing separator, and anycombinations thereof.

In one embodiment of an apparatus for reducing air pollutants fromcombustion engines includes a first end, a second end, and a middleportion, wherein the first end includes a connector capable of beingadapted to the intake of a combustion engine, the second end includes aninterface exposed to an air source; and the middle portion communicatesair from the second end to the first end and includes an oxygenenhancer, wherein the air source is comprised of compressed oxygen.

One embodiment of a method for reducing NO_(x) produced in the exhaustfrom an internal combustion engine upon the combustion of a givenquantity of hydrocarbon fuel in air to provide an engine designed outputpower, includes enriching the oxygen in the intake air to an internalcombustion engine, maintaining the given quantity of hydrocarbon fueland output power at the designed output power for the engine, andcombusting the oxygen enriched air with fuel in the engine at a lowertemperature than the normal combustion temperature for the engine whenburning air having ambient oxygen content, wherein the lower temperaturecomprises a temperature defined by the equation:

Ae ^(−E/RTs) X _(As) X _(B) =ΔC _(A) /Δt=Ae ^(−E/RTe) X _(Ae) X _(B)

-   -   where:    -   A=the activation constant for the combustion reaction;    -   e=is the exponential value;    -   E=is the energy constant for the combustion reaction;    -   R=is the rate constant for the combustion reaction;    -   Ts=is the standard average combustion temperature at which the        engine is designed to burn the fuel to produce the expected        output power;    -   X_(As)=is the concentration of oxidant in the air to be        combusted;    -   ΔC_(A)/Δt=is the rate of conversion of fuel and oxidant to        exhaust gases;    -   Te=is the lower temperature of the combustion to have the same        rate of conversion of fuel and oxidant when the concentration of        oxidant is increased;    -   X_(Ae)=is the increased concentration of oxidant        so that a rate of fuel energy conversion results due to the        oxygen enriched air at the lower temperature that is essentially        the same rate of fuel energy conversion as would normally result        from combusting the fuel with air having ambient oxygen content,        wherein the amount of thermal NO_(x) produced in exhaust gas        from the engine is reduced due to the lower combustion        temperature.

While the invention has been described with respect to a limited numberof embodiments, and the discussion has focuses on motor vehiclecombustion engines, those skilled in the art, having benefit of thisdisclosure, will appreciate that other embodiments can be devised whichdo not depart from the scope of the invention as disclosed herein. Forexample, ship engines that burn fossil fuels may also benefit from thepresent invention. Accordingly, the scope of the invention should belimited only by the attached

What is claimed is:
 1. A method for reducing air pollutants from aninternal combustion engine of the type designed for providing a givenpower output based upon the combustion of hydrocarbon fuel in air, themethod comprising: providing an oxygen-enriched intake air stream to aninternal combustion engine, maintaining the output power at the givenpower output according to the design of the engine, combusting theoxygen enriched air with fuel in the engine at a temperature lower thanthe normal combustion temperature for the engine when burning air havingambient oxygen content so that a rate of fuel energy conversion resultsdue to the oxygen enriched air at the lower temperature that isessentially the same rate of fuel energy conversion as would normallyresult from combusting the fuel with air having ambient oxygen content,wherein the amount of thermal NO_(x) produced in exhaust gas from theengine is reduced due to the lower combustion temperature.
 2. The methodof claim 1, wherein the oxygen-enriched intake air comprises a mixtureof nitrogen and oxygen and the oxygen concentration is at least 25%oxygen.
 3. The method of claim 1, wherein the oxygen-enriched air streamis provided by one or more methods of oxygen-air stream enrichmentselected from the group of oxygen enrichment methods including supplyingcompressed oxygen into the engine air intake, supplying enriched oxygenintake air into the engine by molecular membrane separation of fromenriched oxygen air from enriched nitrogen air, supplying enrichedoxygen intake air into the engine by separating oxygen and nitrogengases using a gas separation membrane, supplying enriched oxygen intakeair into the engine by separating oxygen and nitrogen gases using amolecular sieve, supplying enriched oxygen intake air into the engine byseparating oxygen and nitrogen by using a filter, supplying enrichedoxygen intake air into the engine by separating oxygen and nitrogen byusing a gas absorption separator, supplying enriched oxygen intake airinto the engine by separating oxygen and nitrogen by using a pressureswing separator, and supplying enriched oxygen intake air into theengine by separating oxygen and nitrogen by gases using any combinationsthereof.
 4. A method of improving fuel efficiency in a combustion enginecomprising: adapting an oxygen-enriching apparatus to a combustionengine; providing an air stream from the oxygen-enriching apparatus tothe combustion engine intake; and combusting fuel with theoxygen-enriched air.
 5. An apparatus for reducing air pollutants fromcombustion engines comprising: a first end, a second end, and a middleportion, wherein the first end comprises a connector capable of beingadapted to the intake of a combustion engine; the second end comprisesan interface exposed to an air source; and a middle portioncommunicating air from the second end to the first end and comprising anoxygen enhancer, such that the air communicated from the air source tothe engine has enhanced oxygen content;
 6. The apparatus of claim 5,wherein the oxygen enhancer of the middle portion further comprises oneor more oxygen enhancement mechanisms selected from a molecularmembrane, a gas separation membrane, a molecular sieve, a filter, a gasabsorption separator, a pressure swing separator, and any combinationsthereof.
 7. The apparatus of claim 5, wherein the air source iscomprised of compressed oxygen.
 8. A method for reducing NO_(x) producedin the exhaust from an internal combustion engine upon the combustion ofa given quantity of hydrocarbon fuel in air to provide an enginedesigned output power, the method comprising: enriching the oxygen inthe intake air to an internal combustion engine, maintaining the givenquantity of hydrocarbon fuel and output power at the designed outputpower for the engine, combusting the oxygen enriched air with fuel inthe engine at a lower temperature than the normal combustion temperaturefor the engine when burning air having ambient oxygen content, whereinthe lower temperature comprises a temperature defined by the equation:Ae ^(−E/RTs) X _(As) X _(B) =ΔC _(A) /Δt=Ae ^(−E/RTe) X _(Ae) X _(B)where: A=the activation constant for the combustion reaction; e=is theexponential value; E=is the energy constant for the combustion reaction;R=is the rate constant for the combustion reaction; Ts=is the standardaverage combustion temperature at which the engine is designed to burnthe fuel to produce the expected output power; X_(As)=is theconcentration of oxident in the air to be combusted; ΔC_(A)/Δt=is therate of conversion of fuel and oxidant to exhaust gases; Te=is the lowertemperature of the combustion to have the same rate of conversion offuel and oxidant when the concentration of oxidant is increased;X_(Ae)=is the increased concentration of oxidant; so that a rate of fuelenergy conversion results due to the oxygen enriched air at the lowertemperature that is essentially the same rate of fuel energy conversionas would normally result from combusting the fuel with air havingambient oxygen content, wherein the amount of thermal NO_(x) produced inexhaust gas from the engine is reduced due to the lower combustiontemperature.